Corrosion behavior of steel embedded in calcium sulfoaluminate-cement concrete

Calcium sulphoaluminate cement (CSA) has become in recent years a popular and environmental-friendly alternative to ordinary Portland cement (OPC). A great deal of knowledge has been gained on the microstructure, hydration mechanism, and environmental performance of this innovative binder but there is still lack of knowledge on durability issues related to the use of CSA-concrete. Taking into account that the pore solution of concrete with sulphoaluminate cement has a different alkalinity than that obtained using ordinary portland cement, the protection capacity of such concrete in relation to the corrosion of embedded steel reinforcement needs to be studied. This paper describes the results of an experimental study aimed at investigating the carbonation-induced corrosion of carbon steel reinforcing bars in contact with a CSA-based concrete. Concrete produced using a commercial calcium sulphoaluminate cement and, for comparison, with a reference Portland-limestone cement was characterized in terms of compressive strength, electrical resistivity and carbonation rate tests. Furthermore, electrochemical tests were carried out to measure the corrosion potential and the corrosion rate of steel. Results showed that the pore solution of sulphoaluminate-based concrete is alkaline and induces passivation on embedded carbon steel. Even when the concrete was carbonated, negligible values of corrosion rate were measured on embedded steel exposed up to 95% relative humidity at 20°C. Corrosion rate of steel in carbonated CSA-concrete reached high values when concrete specimens were saturated by water.